(1) Field of the Invention
This invention relates to ramps and, in particular, to collapsible ramps capable of attaching to or folding into or onto the tailgate of a pickup truck.
(2) Prior Art
Various types of collapsible ramps are developed for use with motor vehicles and the like. It is known to provide ramps which can be collapsed down to a pack which is able to be attached to or nest within the volume of a pickup truck tailgate.
In U.S. Pat. No. 4,527,941, a lazy tong mechanism is used to enable a number of planks or panels to be collapsed into a pack at the rear of the vehicle for extension therefrom. The lazy tong structure is not readily adapted for load bearing and the collapsed pack it establishes has a substantial width. U.S. Pat. No. 4,571,144 is another lazy tong structure but this time mounted to the tailgate rather than to the vehicle floor as in U.S. Pat. No. 4,527,941. Again, this structure is not readily strengthened and it is not adapted for collapsing into a thin pack which does not add substantially to the volume of the tailgate.
In U.S. Pat. No. 4,864,673, a telescoped deck is extended out over a foldable support. Strength under load is achieved through the foldable support. Load bearing is essentially achieved by a simple beam which will bend under load unless considerable cross-sectional dimensions are used which adds to weight. In U.S. Pat. No. 4,944,546, the panels are hinged to one another to be folded into a pack which in its extended position extends legs to provide for load support. Good load support might be achieved this way but the ramp is only useful on level ground able to support the legs.
In U.S. Pat. No. 4,761,847 is shown a portable ramp comprised of hinged panels which are supported under load by a system of cables holding the panels at 180.degree. against further folding downwards with the load at the hinges. However, U.S. Pat. No. 4,761,847 does not describe how a multiple hinged ramp would be strengthened this way and collapsed into a compact pack useful as a tailgate ramp.
In U.S. Pat. No. 3,976,209 to Burton, there is described a two panel ramp (three if the tailgate panel is counted) with hinges enabling collapse into a vehicle tailgate. At one hinge, a system of struts equivalent to the cables of U.S. Pat. No. 4,61,847 provides load bearing support. At the other hinge, support is achieved from the tailgate sides by angular displacement limiting ties. U.S. Pat. No. 3,976,209 is limited to three panels and as these have a length equal to the tailgate height, the length of the ramp is determined.